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W. A. KNAPP. PROCESS OF FITTING CAST IRON ARTICLES TO OTHER BODIES IN CONNECTION WITH WHI APPLICATION FILED OCT-1.1915. RENEWED DEC. 19.1918.

Patented June 2-1, 1919.

II I I a I M mama.

UNITED STATES, PATENT OFFICE WILLIAM A. KNAPROF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR, BY DIRECT I AND MESNE ASSIGNMENTS, TO DISTRICT OF COLUMBIA .PROCESS OF FITTING CAST-IRON ARTICLES TO OTHER BODIES IN CONNECTION WITH WHICH THEY WORK, PRODUCT OF SUCH PROCESS. I

Specification of Letters Patent. Patented June 24, 1919 Application filed October 7,1915, Serial No. 54313; Renewed December 19, 1918. Serial No. 267,538.

i citizen of the United States, residing at Washington, District of Columbia, have in-- Vented certain new and useful improvements in processes of fitting cast-iron articles to other bodies in connection with which they work, and .products of such processes, of which the following is a specification.

My invention relates to a process of treatling finished cast iron articlesby. which they are permanently. heat-expanded, and consists of the process herein to be described and to the products of such process, I have discovered that iron castings, when subjected to a red heat and then allowed to cool slowly, may become permanently expanded, that is to say, they do not, upon cooling, contract to the same sizes as they had before being heated, but remain permanently enlarged to a perceptible degree. I

believe that this is true of all kinds of iron castings, butthe tendency to expand permanently is particularly pronounced in hollow castings, and more especially in those of cylindrical form, such as gas engine'pistons. Furthermore, I have also discovered that castingsso expanded may be again permajnently expanded and the process repeated until a substantial degree of enlargement is secured.

- I haveappl ied my invention practically to the expanslon and refit-ting of. worn or loose cast iron engine pistons, particularly to the pistons of gas engines, and more especially to those of engines used upon motor vehicles; and I shall in this application describe the process in connection with the expanding and refitting of such pistons, al-

though the principle of the invention may be applied to advantage to the fitting of new pistons and cylinders, and to the expandin and fitting of other articles than pistons.

][n the accompanying drawings- 4 Figure 1 is'a longitudinal sectional View" through the cylinder of an internal combustion engine, which has been used until the cylinder has become so worn that-the piston no longer'fits it accurately and tightly, the View being largely diagrammatic in its character, and the showing of the extent to which the cylinder is worn exaggerated;

Fig. is a yiew illustrating one method of heating a piston to expand it; and

F g. 3 is an elevation illustrative of the -cool1ng step of the process.

, In the expanding of an ordinary iron castin,fs1ich as the piston of an engine, I heat it to a temperature of between 1400 and lGOOdegrees F. This heating may be in a furnace or a retort, or it may be by means of.

cation of heat is discontinued and the casting allowed to cool slowly. This may be accomplished by removing the torch and coveringthe open end of the piston, as by means of a sheet of asbestos, suchas indicated at e in Fig. 3. The jacket band coi-*ering e not only insure a gradual and uniform cooling, but largely operate to prevent access of air to the article a, thus reducing the liability ofthe surfaces of the piston becoming oxi dized and scaling.

On becoming cooled the casting will be found to have expanded slightly in all directions, and this expansion 1 have discovered remains permanent. If the expansion secured by a single heat treatment as de-. scrlbed is insufficient for the purpose in view,

the, treatment is repeated, with the-result that the casting will be again, and further, enlarged, the second eiipansion being also permanent, and this alternate heatin and cooling may be carried on with sa ety a number of times so as to secure a considerable enlargement of the article.

One extremely useful and valuable application of my invention is to-the refitting of pistons to engine cylinders where one or both have become worn. I refer to Fig. 1 of the drawings where a indicates the piston of a gas engine, and f the cylinder in which it works, these, particularly the cylinder, havin'g become, through use, so worm that the CHARLESSCHWARTZ, TRUSTEE, OF WASHINGTON,

- piston no longer fits the cylinder tightly. In practice the piston of a gas engine becomes somewhat reduced indiameter through wear,

and the cylinder in which it works becomes enlarged, particularly at those parts opposite which the piston travels, as indicated at g r in Fig.1, sothat the cylinder becomes larger thus equipped.

at the rear parts 9. than at the front por tion it. Then this occurs it is now thecommon practice to obtain anew oversize plston, and to rebore the cylinder to fit such 1 1 piston. T his practice is expensive and not always satisfactory, as the reboring is often attempted upon a machine. not especially in-.

tended forthat purpose, with the resultthat the engine cylinders are frequently seriously injured. Furthermore, the balance of the engine by the use of an oversize piston is disturbed, and this .is believedby some to injpriou sly affect the running of an engine By the use of my invention I am enabled to overcome the objections to the use of an oversize piston replaci'ng one that has become worn, to materially reduce the expense incident to the installation of such a piston,

and to insure a uniformly better result. To secure this I expand the worn piston, according to the method 'already herein described, until it is of a'size to fit quite closely the front or outer end portion 7?. of thecylinder-thepartthat is ordinarily least worn.

I the piston is a second time expand'edand the I then insert this expanded piston into'the openend of the cylinder, and grindthe latter, by 'means of the piston, using some abrasive between them, taking off the high places and irregularities of the cylinder and bringing it to true cylindrical shape and to a slightly greater diameter than it originally had. 'If a single grinding be not sufficient grinding and shaping process just described repeated, and this is continued until the cyhnder'throughout its working portion is brought to truecylindrical'shape and of the.

desired diameter to fit the piston. Two or three alternate expandingand grinding operations have been usually, found to be sufficient to restore a considerably worn cylinder to good working condition, Should the expansion of the piston at any time be found toogreat to permit of its insertion into the end it of the cylinder, it may be reduced in diameter by turning. Not onl is the process useful in refitting old pistons to cold cylinders, but it will be found of advantage,

in obtaininga perfect fit between new cylinders a-nd HOWPIStOTIS.

It well understood that a better fit is obtained by grinding two parts together than where ityis sought to secure thefdesiredresult byturning'processes alone, and by my process the fitting, of cyl1nder and piston, is easily made practlcally possible.

by the grinding together The temperatures to which the articles being treated according to my process are heated, hereinbefore mentioned, that is, between.

atur, or one between that and 1400 F. may

.be, to advantage employed where a very slight expansion is desired. While I am not now able to fix the limits of temperature for heating the articles when practising my process, with accuracy, I believe that the term red heat describes with approximate accuracy the range of temperatures available for the heating step of the process.

' It is evident that-the specific gravity of an article expanded according to my process is less than that of ordinarycast iron, that is, "cast iron that has not been expanded. I

have expanded hollow pistons for internal combustionengines to a degree that perceptibly,lowered their specific gravity, without, ,so far as I have been able to determine, impairing the strength and working qualities of the pistons, while, because of the lessened. .weight for size, such expansion has been of advantage.

VVhatI claim is I 1. The herein described process of fitting a L cast iron article to another body in connection with which it works, which consists in permanently heat-expanding the article to a size approximating that it should have in order to properly work in cooperation with the other body,'and then grindin the two together to accurately fit one anot ier.

2. The process of enlarging and bringing to desired shape finished cast iron articles that have become wornin use, which consists in subjecting the articles to heat treatment by which they are permanently expanded to the desired size and then operating upon their surfaces to bring them to the finished shape and form desired.

cast iron piston tov a cylinder in connection with which'it is to work, which consists in, permanently heat-expanding the piston to approximately-the desired size, then grind- ;3. The herein described process of fitting a ing'it and the cylinder together to cause them to accurately fit one another.

41 The herein described process of refitting a worn cast iron piston to a cylinder in which it works, which consists in first permanently expanding the piston to a size to closely fit an endofthe cylinder-"into which it may be inserted, then introducing such expanded piston into the cylinder and grinding them together; then a second time permanently heat-expanding the piston and reintroducing it into the cylinder and grinding the two together, and repeating these steps until the cylinder is properly reshaped.

5. The process of fitting an engine piston to a cylinder in which it works which consists in first permanently expanding a finished piston to a size to closely fit the bore of the cylinder, and then subjecting it to surface treatment to shape it to the cylinder.

6. The herein described process of refitting worn cast iron pistons to cylinders in which they work, whichconsists in pern1a-' nently expanding the piston to a size to closely fit an end of the cylinder into which it may be inserted, and then introducing the piston into the cylinder and grinding them together to cause them, to accurately fit one another.

7. The herein described process of refitting worn cast iron pistons to cylinders in which expanding the piston to a size to closely fit an end of the cylinder into which it may be *inserted, then introducing the piston into the cylinder and grinding them together,

and repeating these steps until the cylinder is reduced to cylindrical form throughout the working stroke of the piston and the lat ter is expanded to fit the reshaped cylinder.

8. A new article of manufacture consisting of a castiron engine piston permanently heat-expanded to working size and having its working surface ground to fit the cylinder in which it is to work.

9. A new article of manufacture consisting of a hollow, cast iron, engine piston-permanently heat-expanded to working size and of a specific gravity less than that of ordinary cast iron, and havingits working surface operated upon to finish it to fit the cylinder in which itis to WOIk;

WILLIAM A. KNAPP. 

